I haven’t really looked into it, but isn’t an audio amplifier a voltage amplifier? Relay testing requires high currents, along with normal and reduced voltages. Pretty sure that if there was an easy out there wouldn’t be nearly so many people buying relay test sets at the prices relay test sets go for.
The test sets provide an accurate time to trip, which may be lacking in an audio transformer.
Will you add a sine wave generator or scale down grid power for a sine wave input?
Does the amplifier introduce a phase shift?
Some types of protection relays are sensitive to phase angle.
Once you have a suitable transformer, why no just drive the transformer through a ballast resistor with a Variac?
Of course that still leaves the timing issue.
Bill
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"Why not the best?"
Jimmy Carter
Q. "...Anybody used audio power amplifier for protection relay test? "
A1. If you check the basic specification of commercial (simple/basic) single-phase relay test sets on the market, in general, having variable ac, dc (voltage) output say 0.01-500V, variable ac, dc (current) output say 0.01-50Adc, 0.01-100Aac. A volt meter, a current meter and a timer say 0.001-9999s. A toggle switch for stopping the timer (time-delay-to-close) or (time-delay-to-open). Some resistors for voltage divider and capacitors for phase-shift applications. More advance types may operate on single-phase input, three-phase output generated internally. These advance types have phase-shift indication with recording features etc....
A2. In general, there is no (audible announcement).
A3. Please advise what is your application and why the use of "audio power amplifier".
Che Kuan Yau (Singapore)
I have been down similar roads with a self made kit, never an audio amplifier, but a variac, phantom load, etc. I don't miss those days. In my case it may have been because I drove 5 hours and went to use regular kit and it failed. or some special application.
You haven't mentioned a timer, but it was mentioned above and, of course is an important part of the test. You haven't mentioned who owns the relays being tested, but calibration is something else to consider. How are you measuring the output? Are you considering the additive deviations (clamp/shunt + meter, etc).
Most purpose built relay test sets have some degree of safety / overload / open circuit / short circuit protection for these test set and user. If you choose to build your own, consider adding some protection for your ket and yourself.
